The June 1 wedding of Napster co-founder and first Facebook president Sean Parker is turning into a full-scale Hollywood production. Sources tell us the cost of his nuptials to petite singer Alexandra Lenas is now upward of $9 million. The costumed affair — which will have every guest arriving in their own custom-made outfit — will take place in California.

A source told us: “Sean is so excited about the wedding he doesn’t care about the cost. He has invited around 300 people, all his friends and business contacts. The affair is so large they’re building their own structures. They have also blocked out numerous hotels in Big Sur for the guests to stay for the event, which will be a multiday affair.”

Local reports say wedding planners have been emptying the showrooms of antique and interior décor emporium Jan de Luz. And Parker has hired a landscaping company to build a multimillion-dollar backdrop, complete with a rustic cottage, fake waterfalls, bridges, ruins and ponds.

Page Six first revealed Parker was planning a big fantasy affair and had hired Ngila Dickson, the costume designer for “The Lord of the Rings.” Following our story, he jokingly tweeted, “Just because we don’t trust our guests to dress themselves properly doesn’t mean we want them to look like #GoT [‘Game of Thrones’] characters.”

Meanwhile, Parker and Lenas are staying at The Plaza for up to two years while their townhouse is being renovated. His rep declined to comment. Another source familiar with the wedding plans tells us that after word leaked that the wedding was to take place at the Ventana Inn and Spa, the couple may be moving the event to another location, possibly Pebble Beach, and even the date may be changed.